pH Optimal Values (NEET-Critical Numbers)
| Enzyme | Optimal pH | Location |
|---|---|---|
| Salivary amylase (ptyalin) | 6.8 | Mouth |
| Gastric lipase | 4.0–5.0 | Stomach |
| Pepsin | 1.5–2.0 | Stomach |
| Enterokinase | 7.0–8.0 | Duodenum |
| Trypsin | 7.5–8.5 | Duodenum/Jejunum |
| Chymotrypsin | 7.5–8.5 | Duodenum/Jejunum |
| Carboxypeptidase | 7.5–8.0 | Duodenum/Jejunum |
| Elastase | 8.0–8.5 | Duodenum/Jejunum |
| Pancreatic lipase | 7.5–8.0 | Duodenum/Jejunum |
| Pancreatic amylase | 7.0–8.0 | Duodenum/Jejunum |
| Brush border enzymes (maltase, sucrase, lactase, etc.) | 7.0–8.0 | Jejunum/Ileum brush border |
pH Along the GI Tract
| Organ | Approximate pH |
|---|---|
| Saliva / Mouth | 6.5–7.0 (salivary amylase optimum: 6.8) |
| Stomach | 1.5–2.0 (created by HCl from parietal cells) |
| Duodenum (after bicarbonate) | 7.0–8.0 |
| Jejunum / Ileum | 7.0–8.0 |
| Large Intestine | 5.5–7.0 (acidic due to bacterial fermentation) |
Key Numerical Values
| Value | Number |
|---|---|
| Surface area amplification by villi + microvilli | ~600-fold |
| Small intestine length (approximately) | 6–7 metres |
| Large intestine absorbs water daily | ~1.3–1.8 L |
| Fluid entering large intestine daily | ~9 L |
| Bile salts recycled in enterohepatic circulation | ~95% |
| Bile salt reuse cycles per day | 15–20 times |
| Salivary gland pairs | 3 pairs (parotid, sublingual, submandibular) |
Enzyme Substrates and Products
| Enzyme | Substrate | Product |
|---|---|---|
| Salivary amylase | Starch | Maltose + limit dextrins |
| Pepsin | Proteins | Large peptides |
| Gastric lipase | Short-chain triglycerides | Fatty acids + glycerol |
| Trypsin | Proteins, peptides | Smaller peptides |
| Chymotrypsin | Proteins, peptides | Smaller peptides |
| Carboxypeptidase | Peptides (C-terminal) | Amino acids + shorter peptides |
| Elastase | Elastin | Peptide fragments |
| Pancreatic lipase | Emulsified triglycerides | Fatty acids + monoglycerides |
| Pancreatic amylase | Starch, glycogen | Maltose + limit dextrins |
| DNase/RNase | DNA/RNA | Nucleotides |
| Maltase | Maltose | 2 Glucose |
| Sucrase | Sucrose | Glucose + Fructose |
| Lactase | Lactose | Glucose + Galactose |
| Aminopeptidase | Peptides (N-terminal) | Amino acids |
| Dipeptidases | Dipeptides | 2 Amino acids |